Once you enter into battle regimen mode you should be able to continue attacking (soon auto-attacking) or casting magic while waiting on everyone else to join in. One problem that I see with this is people executing the battle regimen while someone is mid-cast/mid-ability.

I can think of 4 options to fix this issue:

1. Once regimen is triggered it would cancel out all other current abilities/spells being used

2.Wait until everyone goes idle after executing the regimen to trigger button and then execute.

3. Have a message pop in the log saying " %playername% currently busy%" and not allow regimen to go until everyone goes idle

4. Battle regimen will execute minus the person(s) busy in another action

I'd like to see everyone join in quickly with weapon skills AND THEN buff themselves while waiting for others (example: raging strike, hawk eye, absorb attack).